As I had posted in a different thread, it appears to be a Gnome limitation.
I've had this issue in every Distro (even Ubuntu Gnome) except for Fedora.
Although on Lubuntu (I know, Ubuntu with LXDE) and in the Unity DE it was fine.
At least since Windows 8, you can also use Win+Space to change the language (my laptop sports Win 10, as I am also an Insider).
To anyone who doesn't know what the Win key is (yes, I know that this sentence sounds odd, however I've met Mac users who had no idea), it's the equivalent of the Super key, and which sports the Windows logo on most keyboards in the world.
I only learned what the Super key is slightly less than half a decade ago, when I had received an old iMac G3 to tinker about.
Accidentally corrupted the OS 9 (after updating to 9.2.2, back from 9.0.4) when I had attempted to increase the Finder's memory limit.
Lack of a working disk drive (it didn't work when I had received it) or anything with a FireWire connection (never had any Apple device in the house except for a 3rd gen. iPod nano) prevented me from continuing (It doesn't support booting from USB, despite it being a new-world iMac, and me having already updated it's firmware).
Open Firmware only helped me get information about the situation, Even at Apple, the IT manager had no idea how to help me, since some of the commands were beyond him, and told me that the only ones who could help me are the Apple engineers, but that he had no way to contact them.